Pregnancy Test — Purpose, Procedure & Normal Values | MyMedicPlus

A pregnancy test detects human chorionic gonadotropin (hCG), a glycoprotein hormone produced by the syncytiotrophoblast cells of the developing placenta shortly after a fertilised egg implants into the uterine lining. Implantation occurs approximately 6–12 days after fertilisation, and hCG begins to enter the maternal bloodstream and appears in the urine from about 8–10 days after fertilisation. Home urine tests detect hCG qualitatively — reporting a positive or negative result — using a lateral flow immunochromatographic assay. A blood test (serum beta-hCG) can be qualitative, confirming the presence or absence of hCG, or quantitative, measuring the precise hCG concentration in mIU/mL. Quantitative serum beta-hCG is used to confirm intrauterine pregnancy location, establish gestational age, monitor early pregnancy viability, investigate ectopic pregnancy, and diagnose gestational trophoblastic diseases (hydatidiform mole, choriocarcinoma). In a normally progressing early pregnancy, hCG levels approximately double every 48–72 hours during the first 8–10 weeks before reaching a peak and then declining.

A pregnancy test is ordered when a woman has missed a menstrual period, or experiences symptoms suggestive of early pregnancy including breast tenderness and fullness, nausea (particularly in the morning), frequent urination, fatigue, mild lower abdominal cramps, implantation spotting, or food aversions. It is ordered clinically to confirm suspected intrauterine pregnancy, and critically to investigate suspected ectopic pregnancy — a life-threatening condition in which a fertilised egg implants outside the uterus (usually the fallopian tube) that requires urgent diagnosis and treatment. Serial quantitative hCG measurements are used to monitor a pregnancy that may be failing (miscarriage or ectopic pregnancy), to confirm complete resolution after miscarriage or ectopic treatment, and to detect and monitor gestational trophoblastic disease where very high hCG levels and rapid doubling are characteristic. A pregnancy test is also routinely performed before prescribing medications known to cause fetal harm (teratogens such as methotrexate, isotretinoin, thalidomide) and before undertaking procedures or imaging using ionising radiation.

For a home urine pregnancy test, collect and use the first morning urine (first void of the day) for the most concentrated hCG level and the most accurate result. Avoid drinking large amounts of fluid before testing as this dilutes the urine and lowers the hCG concentration, which can produce a false negative result, particularly in early pregnancy when hCG levels are still low. Wait until the first day of your missed period — or at least 1–2 weeks after unprotected intercourse or fertility treatment — before testing; testing too early increases the chance of a false negative result because hCG has not yet reached the test's detection threshold. Follow the kit instructions precisely — use the test strip immediately after removing it from the foil wrapper and read the result in the specified 1–5 minute window. Results read after 10 minutes are unreliable. For a blood hCG test ordered by a doctor, no special preparation such as fasting is needed; the test can be taken at any time of day.

For a home urine pregnancy test, hold the absorbent tip of the test strip in the urine stream for 5–10 seconds, or alternatively dip the tip into a clean container of collected urine for 5–10 seconds and lay the test flat. A control line confirms the test has worked correctly. The result window shows: one line (negative — hCG not detected at the test's threshold) or two lines (positive — hCG detected, indicating pregnancy), or in digital tests, the words 'Pregnant' or 'Not Pregnant'. Any second line, regardless of how faint, is typically interpreted as a positive result. For a qualitative serum blood test, a venous blood sample of 3–5 mL is drawn by a phlebotomist and tested by immunoassay in a clinical laboratory; results return within 1–4 hours. For a quantitative serum beta-hCG, the same venous blood sample is analysed for exact hCG concentration in mIU/mL; results typically take 2–24 hours depending on the laboratory.

Urine test result interpretation: a positive result (two lines or a 'Pregnant' display) indicates that hCG has been detected at or above the test's threshold (usually 20–25 mIU/mL); a negative result (one control line only) indicates hCG is either absent or below the detection threshold. Blood hCG reference ranges: non-pregnant women and men: less than 5 mIU/mL. In a normally progressing intrauterine pregnancy, hCG rises rapidly in the first trimester: 3–4 weeks gestation: 5–50 mIU/mL; 4–5 weeks: 5–426 mIU/mL; 5–6 weeks: 18–7,340 mIU/mL; 6–7 weeks: 1,080–56,500 mIU/mL; 7–8 weeks: 7,650–229,000 mIU/mL (peak); 9–12 weeks: 25,700–288,000 mIU/mL; second trimester: levels decline to 13,300–254,000 mIU/mL. Declining or plateauing hCG in early pregnancy, particularly when the doubling time exceeds 48–72 hours, may indicate a miscarriage or ectopic pregnancy and requires urgent clinical evaluation and ultrasonography.

Home urine pregnancy tests are greater than 99% accurate when used correctly on or after the first day of a missed period. The blood draw for a serum hCG is a safe, standard venepuncture with minimal risks. False negative results occur most commonly with early testing before hCG reaches the detection threshold, with very dilute urine (early morning testing improves accuracy), or when testing within days of implantation when hCG is still very low. Hook effect — a paradoxically false negative at extremely high hCG levels (molar pregnancy) due to antigen excess saturating the antibody — is rare but possible. False positive results are rare and can occur with: fertility medications containing hCG (ovulation trigger injections such as Pregnyl or Ovitrelle, which can persist in the blood for 7–14 days); recent pregnancy loss where hCG may remain detectable for several weeks; very rarely, hCG-secreting tumours (choriocarcinoma, testicular germ cell tumours). A positive pregnancy test confirms that hCG is present but does not confirm viability, correct intrauterine location, or gestational age — all of which require ultrasound examination.